3D 基础知识（3D Basics）

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2023-12-01

在前一章我们已经看到了如何绘制3d形状，本章教你如何绘制三角形并旋转它。

下面给出的是绘制三角形旋转它的程序。

import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.media.opengl.glu.GLU;
import javax.swing.JFrame;
import com.jogamp.opengl.util.FPSAnimator;
public class Triangle3d implements GLEventListener {
   private GLU glu = new GLU();
   private float rtri = 0.0f;
   @Override
   public void display(GLAutoDrawable drawable) {
      final GL2 gl = drawable.getGL().getGL2();
      // Clear The Screen And The Depth Buffer
      gl.glClear( GL2.GL_COLOR_BUFFER_BIT | GL2.GL_DEPTH_BUFFER_BIT );
      gl.glLoadIdentity(); // Reset The View
      gl.glTranslatef( -0.5f, 0.0f, -6.0f ); // Move the triangle
      gl.glRotatef( rtri, 0.0f, 1.0f, 0.0f );
      gl.glBegin( GL2.GL_TRIANGLES ); 
      //drawing triangle in all dimensions
      // Front
      gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Front)
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green
      gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Left Of Triangle (Front)
      gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue
      gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Right Of Triangle (Front)
      // Right
      gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Right)
      gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue
      gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Left Of Triangle (Right)
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green
      gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Right Of Triangle (Right)
      // Left
      gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Back)
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green
      gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Left Of Triangle (Back)
      gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue
      gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Right Of Triangle (Back)
      //left
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Red
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top Of Triangle (Left)
      gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue
      gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Left Of Triangle (Left)
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green
      gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Right Of Triangle (Left)
      gl.glEnd(); // Done Drawing 3d triangle (Pyramid)
      gl.glFlush();
      rtri += 0.2f;
   }
   @Override
   public void dispose( GLAutoDrawable drawable ) {
      //method body
   }
   @Override
   public void init( GLAutoDrawable drawable ) {
      //method body
   }
   @Override
   public void reshape( GLAutoDrawable drawable, int x, int y, int width, int height ) {
      // TODO Auto-generated method stub
      final GL2 gl = drawable.getGL().getGL2();
      if(height lt;=;)
         height = 1;
      final float h = ( float ) width/( float ) height;
      gl.glViewport( 0, 0, width, height );
      gl.glMatrixMode( GL2.GL_PROJECTION );
      gl.glLoadIdentity();
      glu.gluPerspective( 45.0f, h, 1.0, 20.0 );
      gl.glMatrixMode( GL2.GL_MODELVIEW );
      gl.glLoadIdentity();
   }
   public static void main( String[] args ) {
      // TODO Auto-generated method stub
      final GLProfile profile = GLProfile.get( GLProfile.GL2 );
      GLCapabilities capabilities = new GLCapabilities( profile );
      // The canvas
      final GLCanvas glcanvas = new GLCanvas( capabilities );
      Triangle3d triangle = new Triangle3d();
      glcanvas.addGLEventListener( triangle );
      glcanvas.setSize( 400, 400 );
      final JFrame frame = new JFrame ( "3d Triangle (shallow)" );
      frame.getContentPane().add( glcanvas );
      frame.setSize( frame.getContentPane().getPreferredSize() );
      frame.setVisible( true );
      final FPSAnimator animator = new FPSAnimator(glcanvas,300,true);
      animator.start();
   }
}

编译并执行上述程序时，将生成以下输出。在这里，您可以看到旋转3D三角形的快照。由于该程序不包括深度测试，因此三角形是空心的。

要使三角形固定，您需要使用glEnable(GL_DEPTH_TEST)启用深度测试。启用深度缓冲区会显示空白屏幕。这可以通过使用glClear(GL_COLOR_BUFFERBIT | GL_DEPTH_BUFFER_BIT)方法清除颜色来清除。要在init（）方法或glDisplay()方法中启用深度测试，请编写以下代码 -

public void init(GLAutoDrawable drawable) {
   final GL2 gl = drawable.getGL().getGL2();
   gl.glShadeModel(GL2.GL_SMOOTH);
   gl.glClearColor(0f, 0f, 0f, 0f);
   gl.glClearDepth(1.0f);
   gl.glEnable(GL2.GL_DEPTH_TEST);
   gl.glDepthFunc(GL2.GL_LEQUAL);
   gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST);
 }

下面给出了用深度测试绘制3D三角形的程序。

import javax.media.opengl.GL2;
import javax.media.opengl.GLAutoDrawable;
import javax.media.opengl.GLCapabilities;
import javax.media.opengl.GLEventListener;
import javax.media.opengl.GLProfile;
import javax.media.opengl.awt.GLCanvas;
import javax.media.opengl.glu.GLU;
import javax.swing.JFrame;
import com.jogamp.opengl.util.FPSAnimator;
public class Triangledepthtest implements GLEventListener {
   private GLU glu = new GLU();
   private float rtri = 0.0f; 
   @Override
   public void display( GLAutoDrawable drawable ) {
      final GL2 gl = drawable.getGL().getGL2();
      gl.glShadeModel( GL2.GL_SMOOTH );
      gl.glClearColor( 0f, 0f, 0f, 0f );
      gl.glClearDepth( 1.0f );
      gl.glEnable( GL2.GL_DEPTH_TEST );
      gl.glDepthFunc( GL2.GL_LEQUAL );
      gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST);
      // Clear The Screen And The Depth Buffer
      gl.glClear(GL2.GL_COLOR_BUFFER_BIT | GL2.GL_DEPTH_BUFFER_BIT); 
      gl.glLoadIdentity(); // Reset The View
      gl.glTranslatef( -0.5f,0.0f,-6.0f ); // Move the triangle
      gl.glRotatef( rtri, 0.0f, 1.0f, 0.0f );
      gl.glBegin( GL2.GL_TRIANGLES ); 
      //drawing triangle in all dimensions
      //front
      gl.glColor3f( 1.0f, 0.0f, 0.0f ); // Red
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top
      gl.glColor3f( 0.0f, 1.0f, 0.0f ); // Green
      gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Left
      gl.glColor3f( 0.0f, 0.0f, 1.0f ); // Blue
      gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Right)
      //right
      gl.glColor3f( 1.0f, 0.0f, 0.0f );
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top
      gl.glColor3f( 0.0f, 0.0f, 1.0f );
      gl.glVertex3f( 1.0f, -1.0f, 1.0f ); // Left
      gl.glColor3f( 0.0f, 1.0f, 0.0f );
      gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Right
      //left
      gl.glColor3f( 1.0f, 0.0f, 0.0f );
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top
      gl.glColor3f( 0.0f, 1.0f, 0.0f );
      gl.glVertex3f( 1.0f, -1.0f, -1.0f ); // Left 
      gl.glColor3f( 0.0f, 0.0f, 1.0f );
      gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Right 
      //top
      gl.glColor3f( 0.0f, 1.0f, 0.0f );
      gl.glVertex3f( 1.0f, 2.0f, 0.0f ); // Top
      gl.glColor3f( 0.0f, 0.0f, 1.0f );
      gl.glVertex3f( -1.0f, -1.0f, -1.0f ); // Left
      gl.glColor3f( 0.0f, 1.0f, 0.0f );
      gl.glVertex3f( -1.0f, -1.0f, 1.0f ); // Right
      gl.glEnd(); // Done Drawing 3d triangle (Pyramid)
      gl.glFlush();
      rtri += 0.2f;
   }
   @Override
   public void dispose( GLAutoDrawable drawable ) {
   }
   @Override
   public void init( GLAutoDrawable drawable ) {
      final GL2 gl = drawable.getGL().getGL2();
      gl.glShadeModel( GL2.GL_SMOOTH );
      gl.glClearColor( 0f, 0f, 0f, 0f );
      gl.glClearDepth( 1.0f );
      gl.glEnable( GL2.GL_DEPTH_TEST );
      gl.glDepthFunc( GL2.GL_LEQUAL );
      gl.glHint(GL2.GL_PERSPECTIVE_CORRECTION_HINT, GL2.GL_NICEST );
   }
   @Override
   public void reshape(GLAutoDrawable drawable, int x, int y, int width, int height ) {
      // TODO Auto-generated method stub
      final GL2 gl = drawable.getGL().getGL2();
      if( height <= 0 ) 
         height = 1;
      final float h = ( float ) width/( float ) height;
      gl.glViewport( 0, 0, width, height );
      gl.glMatrixMode( GL2.GL_PROJECTION );
      gl.glLoadIdentity();
      glu.gluPerspective( 45.0f, h, 1.0, 20.0 );
      gl.glMatrixMode( GL2.GL_MODELVIEW );
      gl.glLoadIdentity();
   }
   public static void main( String[] args ) {
      // TODO Auto-generated method stub
      final GLProfile profile = GLProfile.get( GLProfile.GL2 );
      GLCapabilities capabilities = new GLCapabilities( profile );
      // The canvas
      final GLCanvas glcanvas = new GLCanvas( capabilities );
      Triangledepthtest triangledepthtest = new Triangledepthtest();
      glcanvas.addGLEventListener( triangledepthtest );
      glcanvas.setSize( 400, 400 );
      final JFrame frame = new JFrame ( "3d Triangle (solid)" );
      frame.getContentPane().add(glcanvas);
      frame.setSize( frame.getContentPane().getPreferredSize() );
      frame.setVisible( true );
      final FPSAnimator animator = new FPSAnimator( glcanvas, 300,true);
      animator.start();
   }
}

编译并执行上述程序时，将生成以下输出。

在这里，您可以看到旋转3D三角形的快照。由于该程序包含深度测试代码，因此三角形生成实体。